US6294145B1 - Piranha etch preparation having long shelf life and method of making same - Google Patents

Piranha etch preparation having long shelf life and method of making same Download PDF

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Publication number
US6294145B1
US6294145B1 US08/336,352 US33635294A US6294145B1 US 6294145 B1 US6294145 B1 US 6294145B1 US 33635294 A US33635294 A US 33635294A US 6294145 B1 US6294145 B1 US 6294145B1
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volume
oxidizing solution
solution
strong oxidizing
sulfuric acid
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US08/336,352
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Lindsey H. Hall
Charles R. Schraeder
Jennifer A. Sees
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Texas Instruments Inc
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Texas Instruments Inc
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Assigned to TEXAS INSTRUMENTS INCORPORATED reassignment TEXAS INSTRUMENTS INCORPORATED ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HALL, LINDSEY H., SCHRAEDER, CHARLES R., SEES, JENNIFER A.
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B15/00—Peroxides; Peroxyhydrates; Peroxyacids or salts thereof; Superoxides; Ozonides
    • C01B15/055—Peroxyhydrates; Peroxyacids or salts thereof
    • C01B15/06—Peroxyhydrates; Peroxyacids or salts thereof containing sulfur
    • C01B15/08—Peroxysulfates

Definitions

  • This invention relates to a method of providing a strong oxidizing solution containing sulfuric acid and peroxydisulfuric acid or H 2 S 2 O 8 (PDSA) having relatively long shelf life and to the stored strong oxidizing solution.
  • PDSA peroxydisulfuric acid or H 2 S 2 O 8
  • Caro's acid (H 2 SO 5 ) is a powerful oxidizing agent used in preparation of standard piranha etch solutions for use in semiconductor fabrication technologies.
  • the piranha etch solution (Caro's acid) is generally used to remove photoresist from semiconductor devices being fabricated.
  • Pirhana etch solution generally contains from about 4 to about 5 parts by volume concentrated H 2 SO 4 to one part by volume hydrogen peroxide.
  • Caro's acid can be formed by mixing sulfuric acid (H 2 SO 4 ) and hydrogen peroxide (H 2 O 2 ) in a reversible reaction which yields the Caro's acid and water. In the required ratios, this reaction is exothermic, raising the temperature of the bath from ambient to about 110° to about 130° C.
  • Caro's acid formulated in this manner is also relatively unstable and has therefore presented storage problems. In general, when Caro's acid has been required, it has been formulated and used immediately after formulation.
  • Oxidizing solutions have also been produced in the prior art by mixing peroxydisulfuric acid or H 2 S 2 O 8 (PDSA) with sulfuric acid.
  • PDSA peroxydisulfuric acid
  • This formulation has also been found to have poor shelf life because, after about 1 week, there was a 50 percent loss of product where a solution of 10 parts by volume concentrated sulfuric acid to one part by volume PDSA was used. Accordingly, this formulation has only been prepared and applied at the time and point of use.
  • strong oxidizing solution has been formulated and stored with a shelf life in excess of one week. Briefly, this has been accomplished by providing such strong oxidizing solution, preferably by mixing peroxydisulfuric acid having a concentration of from about 2 to about 5 percent and preferably about 4 percent with concentrated sulfuric acid in the ratio of from about 1:8 to about 1:20 parts by volume and preferably 1:10 parts by volume.
  • the acid is then placed in a container which is inert to the chemicals involved, preferably one having high purity and low contamination and of polytetrafluoroethylene (PTFE) or polyfluoroalkoxy (PFA) having an atmosphere which is non-oxidizing and inert to the oxidizing solution or has an evacuated region above the acid.
  • PTFE polytetrafluoroethylene
  • PFA polyfluoroalkoxy
  • the container can then be transported to the point of use and retained at that location for extended periods in excess of one week. While concentrated sulfuric acid and PDSA of from 2 to 5 percent is preferred in the ratios stated above, it is readily apparent that other ratios will be used if less concentrated sulfuric acid is used and/or if PDSA which is more or less concentrated than 4 percent is used.
  • the strong oxidizing solution can be used as a cleaning solution after diluting said solution with water.
  • a 4 percent solution of peroxydisulfuric acid was mixed with a concentrated solution of sulfuric acid in the ratio of 1 part by volume PDSA to ten parts of sulfuric acid.
  • the solution was mixed in a container chemically inert to the chemicals involved, preferably of PFA, to provide a homogeneous mixture and the mixture was immediately stoppered and stored in that container.
  • the ambient gas in the container over the mixture was then removed to the extent possible to provide an evacuated region over the mixture.
  • the container with the mixture was then placed on a shelf at room temperature and tested after one week. The mixture was found to contain 98 percent of its original oxidizing capacity.
  • Example 1 was repeated except that nitrogen was passed into the container to replace the ambient air therein. After one week the mixture contained 98 percent of its original oxidizing capacity.
  • a solution of hydrogen peroxide was mixed with a concentrated solution of sulfuric acid in the ratio of 1 part by volume of 50 percent hydrogen peroxide to 11 parts of sulfuric acid.
  • the solution was mixed in a container chemically inert to the chemicals involved, preferably of PFA, to provide a homogeneous mixture and the mixture was immediately stoppered and stored in that container.
  • the ambient gas in the container over the mixture was then removed to the extent possible to provide an evacuated region over the mixture.
  • the container with the mixture was then placed on a shelf at room temperature and tested after one week. The mixture was found to contain 98 percent of its original oxidizing capacity.
  • Example 3 was repeated except that nitrogen was passed into the container to replace the ambient air therein. After one week the mixture contained 98 percent of its original oxidizing capacity.

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  • Chemical & Material Sciences (AREA)
  • Organic Chemistry (AREA)
  • Inorganic Chemistry (AREA)
  • Cleaning Or Drying Semiconductors (AREA)
  • Detergent Compositions (AREA)

Abstract

A method of formulating a strong oxidizing solution comprising formulating a strong oxidizing solution having from about 2 to about 5 percent PDSA with concentrated sulfuric acid in the ratio of from about 1:8 to about 1:20 parts by volume and storing the strong oxidizing solution in a container having a space over the solution containing one of a vacuum or a non-oxidizing atmosphere inert to the oxidizing solution. The amount of PDSA is preferably about 4 percent by volume and the ratio is preferably about 1:10 parts by volume. The space over the strong oxidizing solution is preferably a vacuum or substantially all nitrogen. Hydrogen peroxide can be substituted for the PDSA in which case the method comprises formulating a strong oxidizing solution having from about 40 to about 60 percent hydrogen peroxide with concentrated sulfuric acid in the ratio of from about 1:8 to about 1:20 parts by volume and storing the strong oxidizing solution in a container having a space over the solution containing one of a vacuum or a non-oxidizing atmosphere inert to the oxidizing solution.

Description

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a method of providing a strong oxidizing solution containing sulfuric acid and peroxydisulfuric acid or H2S2O8 (PDSA) having relatively long shelf life and to the stored strong oxidizing solution.
2. Brief Description of the Prior Art
Caro's acid (H2SO5) is a powerful oxidizing agent used in preparation of standard piranha etch solutions for use in semiconductor fabrication technologies. The piranha etch solution (Caro's acid) is generally used to remove photoresist from semiconductor devices being fabricated. Pirhana etch solution generally contains from about 4 to about 5 parts by volume concentrated H2SO4 to one part by volume hydrogen peroxide. Caro's acid can be formed by mixing sulfuric acid (H2SO4) and hydrogen peroxide (H2O2) in a reversible reaction which yields the Caro's acid and water. In the required ratios, this reaction is exothermic, raising the temperature of the bath from ambient to about 110° to about 130° C. Caro's acid formulated in this manner is also relatively unstable and has therefore presented storage problems. In general, when Caro's acid has been required, it has been formulated and used immediately after formulation.
Oxidizing solutions have also been produced in the prior art by mixing peroxydisulfuric acid or H2S2O8 (PDSA) with sulfuric acid. This formulation has also been found to have poor shelf life because, after about 1 week, there was a 50 percent loss of product where a solution of 10 parts by volume concentrated sulfuric acid to one part by volume PDSA was used. Accordingly, this formulation has only been prepared and applied at the time and point of use.
The economics of piranha solution formulation would be materially improved if the strong oxidizing solution required could be an off-the-shelf item with materially extended shelf life by storage at the point of use rather than having to be formulated separately in conjunction with each use. Not only is the cost of preparation of strong oxidizing solution high but the cost of delivery in a pipeline is also quite high.
SUMMARY OF THE INVENTION
In accordance with the present invention, strong oxidizing solution has been formulated and stored with a shelf life in excess of one week. Briefly, this has been accomplished by providing such strong oxidizing solution, preferably by mixing peroxydisulfuric acid having a concentration of from about 2 to about 5 percent and preferably about 4 percent with concentrated sulfuric acid in the ratio of from about 1:8 to about 1:20 parts by volume and preferably 1:10 parts by volume. The acid is then placed in a container which is inert to the chemicals involved, preferably one having high purity and low contamination and of polytetrafluoroethylene (PTFE) or polyfluoroalkoxy (PFA) having an atmosphere which is non-oxidizing and inert to the oxidizing solution or has an evacuated region above the acid. The container can then be transported to the point of use and retained at that location for extended periods in excess of one week. While concentrated sulfuric acid and PDSA of from 2 to 5 percent is preferred in the ratios stated above, it is readily apparent that other ratios will be used if less concentrated sulfuric acid is used and/or if PDSA which is more or less concentrated than 4 percent is used.
The same result with respect to shelf life should be available when formulating a mixture of hydrogen peroxide having a concentration of from about 40 percent to about 60 percent and preferably 50 percent with concentrated sulfuric acid having a ratio of from about 1:8 to about 1:20 parts by volume and preferably 1:11 parts by volume.
The strong oxidizing solution can be used as a cleaning solution after diluting said solution with water.
DESCRIPTION OF THE PREFERRED EMBODIMENT EXAMPLE 1
A 4 percent solution of peroxydisulfuric acid was mixed with a concentrated solution of sulfuric acid in the ratio of 1 part by volume PDSA to ten parts of sulfuric acid. The solution was mixed in a container chemically inert to the chemicals involved, preferably of PFA, to provide a homogeneous mixture and the mixture was immediately stoppered and stored in that container. The ambient gas in the container over the mixture was then removed to the extent possible to provide an evacuated region over the mixture. The container with the mixture was then placed on a shelf at room temperature and tested after one week. The mixture was found to contain 98 percent of its original oxidizing capacity.
EXAMPLE 2
Example 1 was repeated except that nitrogen was passed into the container to replace the ambient air therein. After one week the mixture contained 98 percent of its original oxidizing capacity.
EXAMPLE 3
A solution of hydrogen peroxide was mixed with a concentrated solution of sulfuric acid in the ratio of 1 part by volume of 50 percent hydrogen peroxide to 11 parts of sulfuric acid. The solution was mixed in a container chemically inert to the chemicals involved, preferably of PFA, to provide a homogeneous mixture and the mixture was immediately stoppered and stored in that container. The ambient gas in the container over the mixture was then removed to the extent possible to provide an evacuated region over the mixture. The container with the mixture was then placed on a shelf at room temperature and tested after one week. The mixture was found to contain 98 percent of its original oxidizing capacity.
EXAMPLE 4
Example 3 was repeated except that nitrogen was passed into the container to replace the ambient air therein. After one week the mixture contained 98 percent of its original oxidizing capacity.
Though the invention has been described with respect to a specific preferred embodiment thereof, many variations and modifications will immediately become apparent to those skilled in the art. It is therefore the intention that the appended claims be interpreted as broadly as possible in view of the prior art to include all such variations and modifications.

Claims (8)

What is claimed is:
1. A method of formulating a strong oxidizing solution of Caro's acid which comprises the steps of:
(a) formulating a strong oxidizing solution of Caro's acid by mixing about 2 to 5 percent PDSA by volume with concentrated sulfuric acid in the radio of about 1 part PDSA: 8 parts sulfuric acid by volume to about 1 part PDSA: 20 parts sulfuric acid by volume; and
(b) storing said strong oxidizing solution in a container having a space over said solution containing one of a vacuum or a non-oxidizing atmosphere inert to said oxidizing solution.
2. The method of claim 1 wherein said PDSA is about 4 percent by volume and said ratio is about 1 part PDSA: 10 parts sulfuric acid by volume.
3. The method of claim 2 wherein said space over said strong oxidizing solution is substantially all nitrogen.
4. The method of claim 1 wherein said space over said strong oxidizing solution is substantially all nitrogen.
5. A method of formulating a strong oxidizing solution of Caro's acid which comprises the steps of:
(a) formulating a strong oxidizing solution of Caro's acid by mixing about 40 to 60 percent hydrogen peroxide by volume with concentrated sulfuric acid in the ratio of about 1 part hydrogen peroxide: 8 parts sulfuric acid by volume to about 1 part hydrogen peroxide: 20 parts sulfuric acid by volume; and
(b) storing said strong oxidizing solution in a container having a space over said solution containing one of a vacuum or a non-oxidizing atmosphere inert to said oxidizing solution.
6. The method of claim 5 wherein said hydrogen peroxide is about 50 percent by volume and said ratio is about 1 part hydrogen peroxide: 11 parts sulfuric acid by volume.
7. The method of claim 6 wherein said space over said strong oxidizing solution is substantially all nitrogen.
8. The method of claim 5 wherein said space over said strong oxidizing solution is substantially all nitrogen.
US08/336,352 1994-11-08 1994-11-08 Piranha etch preparation having long shelf life and method of making same Expired - Lifetime US6294145B1 (en)

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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006029363A1 (en) * 2004-09-09 2006-03-16 Honeywell International Inc. Methods of cleaning optical substrates
WO2008088559A1 (en) * 2007-01-18 2008-07-24 Silicon Genesis Corporation Method and structure for cleaning surfaces for bonding layer transfer substrates
EP1950326A1 (en) 2007-01-29 2008-07-30 Interuniversitair Microelektronica Centrum Method for removal of bulk metal contamination from III-V semiconductor substrates
EP2190967A2 (en) * 2007-08-20 2010-06-02 Advanced Technology Materials, Inc. Composition and method for removing ion-implanted photoresist
EP2288965A2 (en) * 2008-05-01 2011-03-02 Advanced Technology Materials, Inc. Low ph mixtures for the removal of high density implanted resist

Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2899272A (en) * 1957-11-04 1959-08-11 Production of persulfates
US3801512A (en) * 1971-11-18 1974-04-02 Du Pont Stabilized acidic hydrogen peroxide solutions
US3927189A (en) * 1974-04-12 1975-12-16 Du Pont Method for making peroxydisulfuric acid and salts thereof
US3931396A (en) * 1973-05-31 1976-01-06 Commissariat A L'energie Atomique Method of preparation of a composition having a base of 99m technetium for diagnosis by scintigraphy
US4022703A (en) * 1975-01-14 1977-05-10 Produits Chimiques Ugine Kuhlmann Stabilization of hydrogen peroxide in acid baths for cleaning metals
US4229544A (en) * 1978-08-08 1980-10-21 Payfer Laboratories Inc. Living organism packaging
US4334610A (en) * 1979-01-23 1982-06-15 Nissan Chemical Industries, Ltd. Method of storing a solid chlorinating agent and an article for storing same
US4526650A (en) * 1983-01-25 1985-07-02 Outokumpu Oy Method for regenerating pickling acids
US4579725A (en) * 1983-12-30 1986-04-01 E. I. Du Pont De Nemours And Company Potassium monopersulfate compositions and process for preparing them
US4917122A (en) * 1986-08-09 1990-04-17 Micro-Image Technology Limited Compositions for use in the production of integrated circuits and method for its preparation and use
US5304360A (en) * 1990-10-27 1994-04-19 Interox Chemicals Limited Peroxoacid manufacture

Patent Citations (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2899272A (en) * 1957-11-04 1959-08-11 Production of persulfates
US3801512A (en) * 1971-11-18 1974-04-02 Du Pont Stabilized acidic hydrogen peroxide solutions
US3931396A (en) * 1973-05-31 1976-01-06 Commissariat A L'energie Atomique Method of preparation of a composition having a base of 99m technetium for diagnosis by scintigraphy
US3927189A (en) * 1974-04-12 1975-12-16 Du Pont Method for making peroxydisulfuric acid and salts thereof
US4022703A (en) * 1975-01-14 1977-05-10 Produits Chimiques Ugine Kuhlmann Stabilization of hydrogen peroxide in acid baths for cleaning metals
US4229544A (en) * 1978-08-08 1980-10-21 Payfer Laboratories Inc. Living organism packaging
US4334610A (en) * 1979-01-23 1982-06-15 Nissan Chemical Industries, Ltd. Method of storing a solid chlorinating agent and an article for storing same
US4526650A (en) * 1983-01-25 1985-07-02 Outokumpu Oy Method for regenerating pickling acids
US4579725A (en) * 1983-12-30 1986-04-01 E. I. Du Pont De Nemours And Company Potassium monopersulfate compositions and process for preparing them
US4917122A (en) * 1986-08-09 1990-04-17 Micro-Image Technology Limited Compositions for use in the production of integrated circuits and method for its preparation and use
US5304360A (en) * 1990-10-27 1994-04-19 Interox Chemicals Limited Peroxoacid manufacture

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006029363A1 (en) * 2004-09-09 2006-03-16 Honeywell International Inc. Methods of cleaning optical substrates
WO2008088559A1 (en) * 2007-01-18 2008-07-24 Silicon Genesis Corporation Method and structure for cleaning surfaces for bonding layer transfer substrates
EP1950326A1 (en) 2007-01-29 2008-07-30 Interuniversitair Microelektronica Centrum Method for removal of bulk metal contamination from III-V semiconductor substrates
US20080214013A1 (en) * 2007-01-29 2008-09-04 Interuniversitair Microelektronica Centrum Vzw (Imec) Method for Removal of Bulk Metal Contamination from III-V Semiconductor Substrates
US8288291B2 (en) 2007-01-29 2012-10-16 Imec Method for removal of bulk metal contamination from III-V semiconductor substrates
EP2190967A2 (en) * 2007-08-20 2010-06-02 Advanced Technology Materials, Inc. Composition and method for removing ion-implanted photoresist
EP2190967A4 (en) * 2007-08-20 2010-10-13 Advanced Tech Materials Composition and method for removing ion-implanted photoresist
US20110039747A1 (en) * 2007-08-20 2011-02-17 Advanced Technology Materials, Inc. Composition and method for removing ion-implanted photoresist
EP2288965A2 (en) * 2008-05-01 2011-03-02 Advanced Technology Materials, Inc. Low ph mixtures for the removal of high density implanted resist
EP2288965A4 (en) * 2008-05-01 2011-08-10 Advanced Tech Materials Low ph mixtures for the removal of high density implanted resist

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